There is known a sanitary device operable for sensing a sensing target such as a human body and controlling instruments based on the sensing result. For instance, a toilet device is provided with a seating sensor for sensing a user seated on the toilet seat. Flushing and other functions of the toilet device are controlled based on the sensing result of the seating sensor. A commonly known example of the seating sensor is a photoelectric sensor.
However, installation of a photoelectric sensor requires providing a translucent window part in e.g. the flush tank or other location and embedding the photoelectric sensor so as to face the window part. Thus, the toilet device is defiled by the window part. Furthermore, this limits the flexibility of design of e.g. the toilet stool and other devices. There is room for improvement on these points.
To solve this problem, there is proposed a multi-functional toilet device operable for sensing a user seated on the toilet seat by a radio wave sensor such as a Doppler sensor. Radio waves transmitted by the Doppler sensor can pass through e.g. resin. Thus, for instance, the Doppler sensor can be installed in the state of being hidden inside e.g. the casing of the toilet device. This can dispense with the window part required for the photoelectric sensor. However, the Doppler sensor and the microwave sensor are sensors for sensing motion. Thus, it is difficult to determine accurately the presence or absence of a stationary sensing target such as a human body. Furthermore, it is difficult to distinguish the unseating motion of the user from fine motions of the seated user.
To solve this problem, Japanese Unexamined Patent Publication No. 2003-279643 proposes a human body sensing device using a plurality of output signals with mutually different phases. The plurality of output signals are full-wave rectified at an arbitrary reference voltage to calculate the trajectory of the maximum of each full-wave rectified signal. The distance between the sensing target and the human body sensing device can be estimated based on this maximum trajectory. This can determine the presence or absence of a stationary sensing target, and can improve the reliability of seating sensing.
However, the aforementioned maximum trajectory oscillates with the distance to the sensing target. This may cause an error in the estimated distance to the sensing target. More specifically, in the case of a toilet device, the sensitivity of seating sensing may be lowered depending on the stationary position of the user. Furthermore, the level of the output signal may change with the closing or opening motion of the toilet lid. The accuracy of seating sensing may be lowered unless the reference voltage is suitably set in response to such change in the level of the output signal.